Amino acid/ja: Difference between revisions

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==Physicochemical properties==

The 20 canonical amino acids can be classified according to their properties. Important factors are charge, [[hydrophilicity]] or [[hydrophobicity]], size, and functional groups. These properties influence [[protein structure]] and [[protein–protein interaction]]s. The water-soluble proteins tend to have their hydrophobic residues ([[leucine|Leu]], [[isoleucine|Ile]], [[valine|Val]], [[phenylalanine|Phe]], and [[tryptophan|Trp]]) buried in the middle of the protein, whereas hydrophilic side chains are exposed to the aqueous solvent. (In [[biochemistry]], a residue refers to a specific [[monomer]] ''within'' the [[polymer]]ic chain of a [[polysaccharide]], protein or [[nucleic acid]].) The [[integral membrane protein]]s tend to have outer rings of exposed [[hydrophobic]] amino acids that anchor them in the [[lipid bilayer]]. Some [[peripheral membrane protein]]s have a patch of hydrophobic amino acids on their surface that sticks to the membrane. In a similar fashion, proteins that have to bind to positively charged molecules have surfaces rich in negatively charged amino acids such as [[glutamate]] and [[aspartate]], while proteins binding to negatively charged molecules have surfaces rich in positively charged amino acids like [[lysine]] and [[arginine]]. For example, lysine and arginine are present in large amounts in the [[Low complexity regions in proteins|low-complexity regions]] of nucleic-acid binding proteins. There are various [[hydrophobicity scale]]s of amino acid residues.